The use of electrically-assisted nucleic acid hybridization is a known technique in the analysis of biological samples containing DNA, e.g. blood, plasma, urine etc. Conventionally, a chip for DNA detection is formed from one of a variety of materials including glass, silica and metal. On the surface of the chip a number of electrical contacts are formed using known techniques. To detect a particular DNA sequence in a biological sample, capture probes consisting of complementary DNA fragments are attached to the chip surface. If a biological sample contains the target DNA, the target DNA will bind to the complementary DNA fragments by hybridization, and various imaging techniques may be used to detect such hybridization and thus the presence in the sample of the target DNA. By applying an electric current to the capture probes, the hybridization process may be accelerated and thus the detection process is also accelerated. This basic hybridization technique is described, for example, in U.S. Pat. No. 5,849,486.